A niche piece of cycling clothing that has been around in some variation for many years, the barrier sock (sometimes described as a wind sock or liner) is an essential item for my comfort.
Made from windproof and breathable fabrics such as WindTex or WindStopper, barrier socks can extend the comfort range about 10 degrees without adding shoe covers. Adding covers or chemical warmers gives you a lot of options.
There are a few variations, but these socks are designed specifically for cycling. The critical feature is fit. The barrier sock needs to be thin enough to go over a light inner sock and still fit your cycling shoe. I’m not a believer in the ‘size up’ for winter shoes if at all possible (that affects a host of issues including cleat placement).
In general, while the materials are similar, barrier socks made for hiking and other outdoor activities are too bulky for most cycling shoes.
For hard efforts these socks offer much better mobility than a shoe cover. I’ve raced many cyclocross races with them.
My current favorite is the Gore Shield Sock. With plenty of stretch, excellent wind protection, and a tiny bit of inside fleecing, it hits all the marks. The retail is about $50, but has been in short supply this season in many sizes.
Past manufacturers have included Bontrager, NorthWave, Sealskinz, and Sugoi. The NorthWave, which seems to be out of production (and may have only been available in Europe), is the warmest of those I’ve used. NorthWave places more fleece on the inside, but is a bit more bulky than the Gore product.
Note that these are not the same as the current ‘water proof’ socks manufactured by Sealskinz and Showers Pass. Those have a knit finish with a membrane between layers. We will be reviewing that style in the near future.